Method and apparatus for computer aided surgery

ABSTRACT

A number of improvements are provided relating to computer aided surgery. The improvement relates to both the methods used during computer aided surgery and the devices used during such procedures. Some of the improvement relate to controlling the selection of which data to display during a procedure and/or how the data is displayed to aid the surgeon. Other improvements relate to the structure of the tools used during a procedure and how the tools can be controlled automatically to improve the efficiency of the procedure. Still other improvements relate to methods of providing feedback during a procedure to improve either the efficiency or quality, or both, for a procedure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/052,569, filed Oct. 11, 2013, titled “Method and Apparatus forComputer Aided Surgery”, Publication No. US-2014-0039520-A1, which is acontinuation of U.S. patent application Ser. No. 11/764,505, filed Jun.18, 2007, titled “Method and Apparatus for Computer Aided Surgery”, nowU.S. Pat. No. 8,560,047, which application claims priority from U.S.Provisional Application No. 60/814,370, filed Jun. 16, 2006, titled“Method and Apparatus for Computer Aided Orthopaedic Surgery”, and U.S.Provisional Application No. 60/827,877, filed Oct. 2, 2006, titled“Method and Apparatus for Computer Aided Surgery”, the disclosures ofeach of which are herein incorporated by reference in their entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference in their entirety to the sameextent as if each individual publication or patent application wasspecifically and individually indicated to be incorporated by reference.

FIELD

The present invention relates to the field of computer assisted surgery.Specifically, the present invention relates to various aspects of asurgical suite in which a computer provides guidance or assistanceduring a surgical procedure.

BACKGROUND

Many surgical procedures are complex procedures requiring numerousalignment jigs and intricate soft tissue procedures. Preparing andplacing the alignment jigs and other preparation is often a significantpart of the procedure. For instance, when performing a total kneereplacement procedure (“TKR”), the prosthesis must be accuratelyimplanted to ensure that the joint surfaces are properly aligned. If thealignment is inaccurate, the misalignment will lead to failure of thejoint, requiring the complex task of replacing one or more portions ofthe knee prosthesis.

To ensure that the prosthesis is accurately implanted, during a TKRprocedure, the surgeon uses a variety of jigs to guide the cutting ofthe femur and the tibia. The jigs are complex devices that requiresignificant time to install on the patient during the surgicalprocedure.

The advent of computer assisted surgery provides the promise ofsimplifying many of the complexities of surgical procedures. In someinstances, the computer may be used to guide the surgeon during theprocess. Although computer assisted surgery holds promise, there arenumerous aspects to be addressed to make a system commercially viable.For instance, in addition to improving the efficiency of the procedures,the quality of the resulting procedures should be addressed.Accordingly, there continues to exist numerous aspects of computerassisted surgery that require improvement to improve the efficiencyand/or quality of the procedure. The end result will encourage medicalprofessionals to migrate toward computer assisted surgical systems.

SUMMARY OF THE DISCLOSURE

In light of the foregoing, a computer assisted surgical suite having anumber of improvements is provided. For instance, a surgical suitehaving a computer and a surgical tool that communicates with thecomputer may be provided. The system also includes a tracking elementfor tracking the position of the surgical tool. In one aspect, thesystem allows the surgeon to perform a surgical procedure on a virtualmodel of the patient using the surgical tool. As the surgeon performsthe procedure on the virtual model, the computer stores the informationregarding the sequence of the steps performed and the position of thesurgical tool during the procedure. Once the surgeon is satisfied withthe results on the virtual model, the stored information can be usedduring the procedure to assist or guide the surgeon.

According to a further aspect, the computer controls operation of thesurgical tool in response to information detected regarding the surgicaltool. For instance, the system may track the position of the surgicaltool relative to the patient. Based on the data regarding the positionof the surgical tool, the computer may send signals to the surgical toolto control the operation of the surgical tool, such as reducing thespeed on the tool or turning the tool on or off.

According to another aspect, the system provides a communication linkbetween the surgical tool and the computer system that allows thesurgical tool to control operation of the computer system and thecomputer system to control operation of the surgical tool.

Another aspect of the system is directed toward the use of the surgicaltool in a free hand procedure to reduce or eliminate the use of jigsduring a procedure. In such a procedure, the computer tracks theposition of the surgical tool relative to the patient and displays theresults on a screen to guide the surgeon in the procedure. In aresection procedure, the system may be configured to identify thepatient tissue with different colors to identify the proximity of thetissue to the resection boundaries. For instance, tissue that is not tobe resected may be illustrated in a red color, so that the surgeon caneasily see that the tissue is not to be resected. Tissue that is to beresected may be illustrated in a green color. Further, tissue at theboundary of the portion to be resected may be illustrated in yellow, sothat the surgeon can easily see that the cuts are getting close to theboundary.

Yet another aspect of the system is directed toward improving thedisplay of information during a surgical procedure. Specifically,depending on which portion of a procedure is being performed, thesurgeon may desire to change the view of the information beingdisplayed. It can be cumbersome to change the view in the middle of aprocedure to a different view. Accordingly, the system can be used toautomatically switch to a particular view based on the position of thesurgical tool. Additionally, the surgeon may program this informationbefore a procedure, or the system can learn to recognize that aparticular surgeon desires a particular view based on inputs from thesurgeon during various procedures.

According to a further aspect, the system provides a method forassessing and improving the quality of a bone cut. For instance, thesystem measures various parameters relating to the quality of a bonecut, such as surface roughness, accuracy of each cut. If the parameterfall within pre-defined limits, the system indicates to the surgeon thatthe resection was successful, so that the prosthesis can be implanted.If one or more parameter falls outside the pre-defined limits, thesystem may calculate the step or steps necessary to correct the bonecuts so that the surgeon can perform the necessary correction.

Another aspect of the invention is directed improving the monitoring ofthe surgical tool. For instance, in certain aspects of computer assistedsurgery, the position of certain surgical tools may be quite importantin assessing the steps necessary during the procedure. However, duringthe procedure, operation of the surgical tool may cause the tool todeflect. The deflection may result in the system misidentifying theactual position of the surgical tool. Accordingly, the present systemmay include one or more sensors for detecting deflection of a portion ofthe surgical tool and an element for modifying the tracking element inresponse to the detected deflection.

A still further aspect of the present invention is directed to a markerthat is used for marking tissue to be resected. The marker includes anactuator that responds to signals from the computer system. A trackingelement provides data to the computer regarding the position of themarker. Based on the position of the marker, the computer controls themarker between an extended position and a retracted position.Specifically, if the computer detects that the marker is on a portion ofthe patient that is to be marked, then the computer controls the markerto extend the marker to the extended position so that a tip of themarker is exposed to mark the patient. Alternatively, if the marker ison a portion of the patient that is not to be marked, the computercontrols the marker to retract the tip of the marker so that the markercannot mark the patient.

The foregoing and other aspects of the present invention are describedin greater detail in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a computer assisted surgical suite.

FIG. 2 is a diagrammatic view of a surgical tool of the surgical suiteof FIG. 1.

FIG. 3 is an alternative diagrammatic view of a computer assistedsurgical suite.

FIG. 4 is a fragmentary view of a surgical tool of the surgical suite ofFIG. 1.

FIG. 5 is an alternative embodiment of the surgical tool illustrated inFIG. 4.

FIG. 6 is plot illustrating data regarding the surface roughness andsurface waviness.

FIG. 7 illustrates a separation of the surface waviness and surfaceroughness of a surface profile.

FIG. 8 is a table illustrating the various potential error in fitting animplant.

FIG. 9 is a measuring block for assessing the fit of an implant.

FIG. 10 illustrates the femur cuts for a total knee replacementprocedure.

FIG. 11 is a diagram illustrating the error angle for bone cuts in atotal knee replacement procedure.

FIG. 12 is a diagram illustrating the steps of a method for programminga surgical robot.

FIG. 13 is a diagrammatic illustration of a navigable marking pen.

FIG. 14 is a registration block for registering tools of a surgicalinstrument.

FIG. 15 is a registration pointer operable in connection with thesurgical suite illustrated in FIG. 1 or FIG. 3.

FIG. 16 is an alternative embodiment of a surgical tool operable inconnection with the surgical suite of FIG. 1 or FIG. 3.

FIG. 17 is a block diagram of the wireless features of the surgicalsuite illustrated in FIG. 3.

FIG. 18 is a top view of an alternative cutting blade operable inconnection with a surgical saw.

FIG. 19 is a bottom view of the cutting blade illustrated in FIG. 18.

DETAILED DESCRIPTION

Referring now to the figures, wherein like elements are numbered alikethroughout, a surgical suite for computer assisted surgery is designatedgenerally 50. The suite 50 includes a first computer 70 forpre-operative use. For example, pre-operative analysis of the patientand selection of various elements may be performed on the firstcomputer. The suite may also include a second computer 80, referred toas the OR computer, which is used during a procedure to assist thesurgeon and/or control one or more surgical instruments. In addition thesuite may include a computer (standalone or collaborating with 80)mounted on the surgical instrument. First computer 70 is provided in thepresent instance, but may be omitted in some configurations because thefunctions of computer 70 are also implemented on OR computer 80, whichcan be a standalone. Moreover the whole ‘pre-surgical planning’ mayeventually happen instantaneously inside the OR. Nevertheless, ifdesired for particular applications, first computer 70 may be used.Furthermore, the micro-processing system of the system 50 can reside inthe cutting instrument. In such a configuration, the computations anduser interface can be performed within a computer on the surgical tool.Such system performs error analysis of location of the cuttinginstrument relative to the ideal cut to be performed, and displayscorrective actions and other information on a screen mounted to theinstrument.

The suite 50 may include a tracking/navigation system that allowstracking in real time of the position in space of several elements,including: (a) the patient's structures, such as the bone or othertissue; (b) the navigable surgical tools, such as the bone saw 100,which is controlled by the surgeon based on information from the ORcomputer 80 or (c) surgeon/assistants system specific tools, such as apointer, registration tools, or other objects. The OR computer 80 mayalso perform some control on the cutting instrument trough theimplemented of the present configuration of the system. Based on thelocation of the tool, the system 80 is able to vary the speed of thesurgical tool 100 as well as turn the tool off to prevent potentialdamage. Additionally, the suite 50 may also include a surgical robot 200that is controlled by the OR computer 80. The features of the navigabletool 100 and the surgical robot 200 may vary. The details of severaldesirable features are described in greater detail below. The variousfeatures can be selected as desired for a particular practice orsituation. In the following description, the only surgical instrumentshown in figures is the navigated saw 100. Nonetheless, many othersinstruments can be controlled and/or navigated as explained above, suchas a drill, burr, scalpel, stylus, or other instrument. Therefore in thefollowing discussion, the system is not limited to the particular tooldescribed, but has application to a wide variety of instruments.

As discussed further below, one exemplary use of the surgical suiteincorporates the use of a virtual model of the portion of the patientupon which a procedure is to be performed. Specifically, prior to aprocedure, a three dimensional model of the relevant portion of thepatient is produced using CT scans, MRI scans or other techniques. Priorto surgery, the surgeon may view and manipulate the patient model toevaluate the strategy for proceeding with the actual procedure.

One potential methodology uses the patient model as a navigation deviceduring a procedure. For instance, prior to a procedure, the surgeon mayanalyze the virtual model of a portion of the patient and map out thetissue to be resected during a procedure. The model is then used toguide the surgeon during the actual procedure. Specifically, during theprocedure a tracking mechanism monitors the progress of the procedureand the results are displayed in real time on the OR computer 80 so thatthe surgeon can see the progress relative to the patient model.

To provide navigation assistance during a procedure, the system 50includes a position detection device 120 that monitors the position ofthe surgical tool 100. The surgical tool 100 includes one or moreposition markers 105 that identify pre-defined points of reference onthe tool. In the present instance the surgical tool includes severalmarkers 105 which, together with some pre-defined points of reference onthe tool, identify the tool and its location.

Although a variety of position tracking systems can be used, oneexemplary system is the NDI Polaris optical measurement system producedby Northern Digital Inc. The system uses a position sensor and bothactive and passive markers. The active markers may be wired sensors thatare electrically connected to the system. The active markers emitinfrared light that is received by the position sensor. The passivemarkers are wireless markers that need not be electrically connected tothe system. The passive markers reflect infrared light back to theposition sensor. Typically, when using passive markers, the positionsensor floods the field of view with infrared light that is thenreflected back to the position sensor from the passive markers. Theposition sensor includes an infrared receiver and it receives lightemitted light from the active markers and reflected light from thepassive markers. The position system triangulates the three dimensionalposition of the tool based on the position of the markers. In thepresent instance, the position detection device 120 is also operable todetect the orientation of the tool relative three orthogonal axes. Inthis way, the position detection device 120 determines the location andorientation of the tool 100.

The position detection device 120 is linked with the OR computer 80 sothat the data regarding the position of the surgical tool 100, thepatient's anatomy, and other system specific tools, is communicated tothe OR computer. The computer uses this information to track theprogress of a procedure.

To track the position of the surgical tool 100 relative to the patient,position marker is attached to the portion of the patient on which theprocedure is to be performed. The position marker attached to thepatient may be similar to the position marker 105 attached to thesurgical tool 100, as shown in FIG. 4. The position marker on thepatient is correlated to a corresponding point on the virtual model ofthe patient. In this way, the registration point positions the toolrelative to the patient and the patient relative to the virtual model.

A series of points are used to register or correlate the position of thepatient's anatomy with the virtual model of the patient. To gather thisinformation, a navigated pointer is used to acquire points at ananatomical landmark or a set of points on a surface within the patient'sanatomy. A process referred to morphing may be used to register thepatient to the virtual model of the patient. During such a process, thesurgeon digitizes parts of the patient and some strategic anatomicallandmarks. The computer 80 analyzes the data and identifies commonanatomical features to thereby identify the location of points on thepatient that correspond to particular points on the virtual model.

Accordingly, as set forth above, the position detector monitors theposition of several items in real time, including: the position of thesurgical tool 100, the position of the patient and the position of itemsused during a procedure, such as a pen or marker as described furtherbelow. Accordingly, the computer combines the data regarding theposition of the surgical tool 100, the data regarding the position ofthe patient, and the data regarding the model of the patient. Thiscombination is used to provide a real time model of the position of thetool relative to the patient, which can be viewed by the surgeon on themonitor. Further still, as previously described, prior to a procedure,the surgeon may analyze the patient model and identify the tissue thatis to be resected. This information can then be used during theprocedure to guide the surgeon.

During the procedure, the monitor displays a model of the surgical toolrelative to the patient model, which reflects the real time position ofthe tools, such as the surgical tool 100, relative to the patient. Thesurgeon can align the position of the tool 100 by viewing the positionof the image of the tool relative to the patient model on screen. Oncethe monitor shows the virtual tool to be aligned with the portion of thepatient model identified for resection, the surgical tool is properlyaligned on the patient. In this way, the doctor can align the toolwithout the need for complex jigs or fixtures. Further, as the tool 100intersects the patient, the data regarding the position of the tool andthe patient model is correlated to show the result of the toolintersecting the patient. In this way, the computer can analyze anddisplay the progress of a procedure in real time. As the tool 100 cutspatient tissue, the monitor displays the tissue being removed from thepatient model. Therefore, in addition to guiding the position of thetool, the OR computer can be used to guide the surgeon as to what tissueshould be resected during a procedure.

In addition to including a surgical tool controlled by the surgeon, thesuite 50 may include a surgical robot 200. The surgical robot can beprogrammed to perform one or more operations during a medical procedure.The surgical robot 200 is controlled by the OR computer, which isprogrammed with the instruction set for the procedure. As with thenavigation system described above, when using the robot, the positiondetection device 120 monitors the position of the surgical robot, andprior to the procedure the location of the patient is identified so thatthe computer has data regarding the position of the surgical robotrelative to the position of the patient.

Assessing and Correcting Bone Cuts

When implanting a prosthetic onto a bone, the surgeon must resectportions of the bone to prepare the bone to receive the prosthetic.Regardless of how the resection is performed, it is important to assessthe quality of the cuts performed during a procedure prior implantingthe prosthetic. Bad fit between the bone and the prosthetic causes asignificant number of implant failures. Therefore, a close match betweenthe shape and dimensions of the prepared bone and the prosthetic isimportant to the proper affixation and durability of the implant. Thesurgeon may rely upon experience and trial and error during a procedure,however, doing so does not provide a quantifiable method for ensuringthat a resection is proper.

Accordingly, it may be desirable to incorporate a method and apparatusfor assessing the quality of bone cuts before a prosthetic is implanted.Additionally, after assessing the bone cuts, it may be desirable toprovide feedback regarding any additional shaping that should be made toimprove the bone cuts to prepare the bone to receive the implant.

The steps for assessing and correcting bone cuts will not be described.First, the bone is resected according to the geometry of the prostheticto be implanted. The resected bone is then scanned in three dimensionsor digitized to obtain a three dimensional image of the bone. Thescanned geometrical image is then analyzed to evaluate various criteriaof the bone cuts. Based on the analysis of the scanned image,suggestions may be provided to the surgeon directly in the operatingroom before the prosthesis is implanted. In this way, the systemprovides feedback to the surgeon to allow for additional modificationsto be made to the resected bone to improve the fit with the prosthesis.

Referring to FIG. 1, the system for assessing the bone cut comprises ascanning device 320 that communicates with a processor, such as apersonal computer, which may be the OR computer 80. The processorcommunicates with an output device, such as a monitor 85 to illustrateinformation about the assessment of the bone cuts.

The scanning device 320 may be one of a number of various devices foracquiring information regarding the three dimensional configuration ofan object. The scanner may use electromagnetic, ultrasonic/acoustic,mechanical, infra-red line-of site, or other elements. For instance, athree dimensional optical laser scanner, scriber, navigated digitizer,coordinate measuring machine or CT-based digitization can be used tocreate a digital model of the bone surface.

The processor analyzes the scanned data to evaluate each cut of theresected bone. For instance, in the case of a TKR procedure, there aretypically five separate cuts made to the femur when the bone is resectedto accommodate the prosthetic (it may be considered seven cuts ratherthan five when considering the posterior condyle resection as two cuts,as well as the posterior chamfer). The image data for the resected boneis analyzed to assess the surface finish for each of the five cuts.During the evaluation of the image data, the processor may evaluateseveral characteristics, including, but not limited to, surface finish,fit error (i.e. looseness), location error (alignment error), and theaccuracy of each cut. Each of these characteristics is discussed belowin greater detail.

Surface finish may include one or more characteristics to evaluatewhether the surface is of sufficient quality to bond well with theprosthetic. In the present instance, the system analyzes the roughnessand/or the waviness of the resected surface to assess the surfacefinish. Roughness includes the finer irregularities of a surface thatgenerally result from a particular cutting tool and material conditions.Waviness includes the more widely spaced deviation of a surface from thenominal or ideal shape of the surface. Waviness is usually produced byinstabilities, such as blade bending, or by deliberate actions duringthe cutting process. As illustrated in FIG. 7, waviness has a longerwavelength than roughness, which is superimposed on the waviness.

Based on analysis of the 3D geometrical image data, the surface finishfor each cut is analyzed and quantified. In the present instance, thesurface finish may be quantified based on: (1) the roughness average,(2) an average of the heights of a select number of the worst peaks(i.e. highest surface peak relative to ideal surface); (3) an average ofthe heights of a select number of the worst valleys (i.e. deepest valleyrelative to ideal surface); and (4) a measure of the deviation from theaverage height of the worst peaks and the average depth of the worstvalley (i.e. (2)-(3)). In some instances, it may be desirable toseparate the quantification of the measure of waviness from the measureof roughness. However, in the present instance, roughness and wavinessare evaluated together. An example of a resected femur havingunacceptable surface finish is illustrated in FIG. 8. As can be seen,the geometry of the resection is proper, so that the prosthetic wouldfit properly onto the resected bone and be properly aligned. However,due to the poor surface finish it is likely that the bond between thebone and the prosthetic will fail prematurely.

In addition to surface finish, it is desirable to analyze the fit errorof resected bone. Fit represents the looseness or play between theimplant and the resected bone shape prior to affixing the prosthetic tothe bone. An example of a resected femur having an unacceptable fiterror is illustrated in FIG. 8. As can be seen, the surface of each cutis acceptable and the orientation of each cut is acceptable, however,the resultant shape leaves unacceptable gaps between the prosthetic andthe resected bone. The gaps create play or looseness that will lead tomisalignment and/or premature failure of the bond between the bone andthe prosthetic.

To measure the fit error, a fitness measuring block 340 may be utilized.The fitness measuring block 340 is a block having an internal shapecorresponding to the internal shape of the prosthetic (i.e. the surfacethat will bond with the bone). A sensor 345 for detecting displacementis attached to the fitness measuring block. In the present instance, thesensor is an infrared tracking device. Alternatively, a navigatedimplant trial that is specific to each prosthetic implant may be usedrather than a measuring block. The navigated implant trial is an implantsimilar to the prosthetic that is to be implanted into the patient. Thenavigated implant includes an element for detecting the position of theimplant trial, such as the sensor 345 described above. The trackingdevice 120 (see FIG. 1) tracks the position of the tracking sensor 345and communicates data to the processor that is indicative ofdisplacement of the fitness measuring block relative to the resectedbone.

The measuring block 340 is placed over the resected bone. The surgeonthen attempts to move the measuring block in all directions relative tothe bone to evaluate translational error based on the amount oftranslation possible between the measuring block and the resected bone.Specifically, the surgeon rotates the block in flexion and extension, aswell as internally and externally. In other words, the surgeon rotatesthe blocks about several axis relative to the bone, such as an axisrunning generally parallel to the axis of the bone (i.e. rotationinternally and externally) as well as an axis running generallytransverse the axis of the bone (i.e. rotation in flexion andextension). As the surgeon moves the measuring block, the sensor detectsthe translational and rotational movement relative to the bone andcommunicates the data with the processor (such as OR computer 80). Basedon the data from the sensor 345 and/or position detection element 120,the processor analyzes and quantifies the fit based on the measuredtranslational error and the measured rotational error.

A third characteristic for assessing the cuts is the location of thecuts, which is the location that the implant may be positioned. Thethird parameter relates to error of the final position case of a tightfit or minimum possible error in case of looseness after the bone is cutand before the prosthetic is cemented. The assessment is performed usingthe same data set that was collected while analyzing the implant fit asdescribed above.

The location error is quantification of the deviation of the location ofthe measuring block from the ideal location at which the implants are tobe positioned. Specifically, in the present instance, the location erroris based on three rotational deviations and three translationaldeviations from the ideal locations. In the case of the trial stage,before drilling the holes for the stems of the implant, only twotranslational errors are considered. The holes are drilled toaccommodate one or more alignment stems that are located on the interiorof the implant. Once the holes are drilled, the holes constrain theposition of the implant relative to the patient. Accordingly, prior todrilling the holes it may be desirable to assess the cuts. Afteranalyzing and/or modifying the cuts, the system may be used to guide theholes to be drilled. As part of the assessment process, the measuringblock is manipulated to account for medial and lateral deviation becauseof constraints in other directions. In this way, depending on theprocedure being analyzed, the directions in which the block ismanipulated may vary.

In the foregoing description, the evaluation of the location error andfit error are based on measurements provided by manipulating the fitmeasurement block 340 relative to the resected bone. Alternatively, thefit and location errors may be evaluated using a virtual comparison ofthe resected bone and models of ideal location and fit for the bone. Forinstance, as described above, the resected bone may be scanned to createa three dimensional model of the resected bone. Prior to the procedure athree dimensional model of the relevant portion of the patient can becreated using any of a variety of techniques, including but not limitedto CT scans and MRI images. The processor may include a database ofmodels corresponding to various prosthetics. The surgeon selects theappropriate prosthetic model and positions it relative to the model ofthe relevant portion of the patient. The processor then modifies thepatient model to reflect the ideal resected surfaces for the selectedprosthetic. Using collision detection algorithms, the scanned data forthe resected bone can be compared with the data for the model for theideal resected bone to calculate the various criteria used to measurefit error and location error.

A final characteristic used in the present instance to evaluate the bonecuts is the accuracy of each cut. For example, in the instance of a TKRprocedure, the accuracy of each cut is evaluated. The importance of theaccuracy of the cuts is exemplified by the third sample illustrated inFIG. 8. As can be seen, the sample has acceptable surface finish, fitand location. In other words, the prosthetic will fit well on the bone(i.e. it won't wiggle excessively), the surface finish is not too roughor wavy and the prosthetic will be properly aligned with the bone.However, due to the inaccuracy in one or more of the cuts, there will begaps between the prosthetic and the bone that will increase thelikelihood of premature failure.

To evaluate the accuracy of the cuts, the deviation between the actualcuts and the ideal cuts for the particular prosthetic is measured. Theideal cuts are determined based on the geometry of the prosthetic to beimplanted on the resected bone. For instance, in the example of a TKR,the ideal cuts for the femur are based on the internal configuration ofthe femoral prosthetic. One way of determining the ideal cuts is tocreate a model of the configuration of the ideal cuts for the patient,as described above

As described above in connection with evaluating the surface finish, inthe present instance, a scanner 320 (shown in FIG. 1) is used to createa model of the resected bone. The data obtained from the scanner 320 foreach planar resected surface is compared with the data for thecorresponding surface of the ideal resected model to evaluate theaccuracy of the cuts. The quantification of the accuracy can be based ona variety of measurements regarding the deviation of each resectedsurface from the ideal surface. In the present instance, fourcharacteristics are measured. The first characteristic is atranslational measurement, and it is calculated as the distance betweenthe plane of the resected surface to the centroid of the correspondingideal cut. The remaining three characteristics are rotational angles.The first rotational characteristic is the orientation of the resectedsurface relative to the ideal plane with respect to a first axis; thesecond rotational characteristic is relative to a second axis and thethird rotational characteristic is relative to a third rotational axis.These characteristics are measured and correlated to quantify theaccuracy of each planar cut of the resected bone.

After the processor determines the various criteria to assess thequality of the cuts, the information regarding the criteria may bedisplayed on the monitor to indicate to the surgeon whether or not thecuts were of sufficient quality to proceed with implanting theprosthetic on the bone. Additionally, if the cuts are not of sufficientquality, the processor may evaluate the cuts to determine a strategy formodifying the resected bone to improve the quality of the cuts. Forinstance, based on a comparison of the scanned data for a resected bonewith the data for the model of an ideal resected bone, the processor maydetermine the portion(s) of bone that should be re-shaped to improve thecorrelation between the resected bone and the model for the idealresected bone. After determining the portions of the bone that should bere-shaped, such changes are displayed on the monitor to show the surgeonwhich portion(s) of the bone should be removed. For example, using agraphical output, the bone may be illustrated generally in white and theportion(s) of the bone that should be resected to improve the fit withthe prosthetic may be shown in red.

In light of the foregoing, the method of assessing the quality of cutsfor a procedure operates as follows. For in-vivo and in-vitroapplications, a three dimensional model of a portion of a patient may begenerated using any of a variety of three-dimensional digitizing,scanning and imaging techniques. The surgeon then selects the element tobe inserted or implanted into the patient and the processor generates amodel of the patient with the location and orientation of the ideal cutsto the respective portion(s) of the patient.

Programming Path for Surgical Robot

As discussed previously, the system provides feedback for a surgeonduring a surgical procedure to aid in guiding the path that the surgeonshould follow during a procedure. Additionally, it may be desirable toprovide the ability to easily define the path that a robot should followduring a procedure.

Referring to FIGS. 1 and 12, a system for programming a surgical robot200 is illustrated. To program the robot, a doctor performs a virtualprocedure on a model of a portion of the patient. The virtual procedureis then translated into a set of instructions that the surgery robotfollows during the actual procedure on the patient.

The system for programming the robot includes a virtual surgerycomputer, such as the pre-op computer 70 and a control computer, such asthe OR computer 80. The control computer communicates with and controlsthe operation of the surgical robot 200. The virtual surgery computer isused to create the instructions for the surgery robot.

In step 450, a virtual model is created for the portion of the patienton which the procedure will be performed. As described above, a virtualmodel can be created using a series of CT scans, MRI scans,interpolating the data among the scans, using statistical procedures,directly digitizing a portion of the patient, or otherwise. The patientmodel is uploaded to the virtual surgery computer and is displayed tothe surgeon in step 455.

The virtual surgery computer includes one or more input devices forinputting information into the computer. For instance, the computer mayinclude a keyboard 75 and one or more position tracking devices 77 sucha mouse or a stylus and pad.

Software on the virtual surgery computer allows the surgeon tomanipulate and perform a virtual procedure on the patient model.Specifically, the software provides an interface so that the surgeon canmanipulate the patient model to view the patient model from differentangles and perspectives. For instance, the surgeon can use the keyboardalone or in combination with the mouse to manipulate the orientation ofthe patient model.

The system may also include the ability to virtually align and place anelement that is to be implanted during the actual procedure. Furtherstill, the location and amount of tissue to be resected may becalculated and displayed on the patient model.

During many surgical procedures, an element is implanted into thepatient. For instance, during an orthopaedic procedure, a prostheticelement is implanted into the patient to replace one or more articularsurfaces in a joint. One example is a total knee replacement (TKR) inwhich surfaces of the knee joint are replaced with a series of kneeprosthetics. The procedure includes the placement of a patellarprosthetic onto the patella, a femoral prosthetic on the end of thefemur and a tibial prosthetic on the tibial plateau. During theplacement of each prosthetic, a portion of the corresponding bone isresected to accommodate the respective prosthetic.

During the actual procedure, the bone to be resected is determined byconfiguration of the prosthetics and the position and orientation of theprosthetics relative to the corresponding tissue. Accordingly, duringthe process of programming the surgical robot, it is desirable toutilize models of the prosthetics. Specifically, the virtual surgerycomputer may include three dimensional models representing the size andshape of various prosthetics.

To incorporate a model of a prosthetic into a virtual procedure, thesurgeon selects a prosthetic and the size for the prosthetic. Typically,during an actual surgery, alignment jigs and fixtures are used toidentify the bone to be resected. Similarly, during a virtual surgerythe model is aligned to the bone (step 457). When performing a virtualsurgery, the software may include alignment tools that are configured toidentify relevant criteria on the tissue that is used to locate andalign the virtual model of the prosthetic. In other words, the virtualalignment tools may operate to automatically align the model of theprosthetic based on a characteristic of the patient model. Thecharacteristic can be automatically identified by the computer based ona set of pre-established criteria for evaluating a patient model, or thecharacteristic can be identified by the surgeon. After the relevantcharacteristic is identified, the alignment tool in the software is usedto identify the location and orientation for the prosthetic model.Alternatively, the surgeon may manually align the model of theprosthetic onto the patient model based on the configuration of theprosthetic and the configuration of the patient.

After the location and orientation of an implant is determined, thecomputer may automatically determine the tissue to be resected (step458). Specifically, the amount of tissue to be resected is determinedbased on the configuration of the prosthetic as known from the model,and based on the orientation and location of the prosthetic asdetermined during the alignment of the prosthetic described above. Byway of example, when implanting a femoral prosthetic, the configurationof the prosthetic is known from the data for the prosthetic model. Oncethe model of the femoral prosthetic is aligned on the model of thepatient, the computer can evaluate the intersection of the prostheticmodel and the model of the patient's femur to determine the location andthe amount of the femur that should be resected to accommodate thefemoral prosthetic. This determination is then displayed on the patientmodel to aid the surgeon in the virtual surgery. For example, if thefemur is displayed as a white solid object, the bone to be resected maybe displayed as a red portion of the femur.

The software also includes onscreen tools that the surgeon can controlvia one or more of the position tracking devices 75, such as a surgicalsaw, a mouse or a pointing device. Further, preferably the softwareprovides a number of different tools that the surgeon can select (step460) during the virtual procedure. The onscreen tool can be as simple asa pointing device that allows the surgeon to trace a path along thepatient model. The path represents the path that the surgeon desires thesurgical robot to follow during the actual procedure. Further, theonscreen tools can be representative of tools that will be used duringthe actual procedure. For instance, the tools may include a cuttingelement, such as a bone cutting saw.

After selecting the appropriate onscreen tool, the surgeon manipulatesthe input device 77 to manipulate the onscreen tool relative to thepatient model (step 465). The surgeon can manipulate both the positionand the orientation of the onscreen tool relative to the patient model.As the onscreen tool is moved relative to the patient model, thesoftware evaluates and displays the result (step 470). For instance, ifthe onscreen tool is a saw and the saw intersects the patient model, thesoftware alters the patient model to show a portion of the patient modelcut and/or removed.

Specifically, based on the coordinates provided by the input device 77,the software determines the position and orientation of the onscreentool relative to the patient model. The software determines whatportions of the onscreen tool and patient model intersect, and at whatangle the tool intersects the patient model. If the onscreen toolintersects the patient model, the software determines the coordinates ofthe intersection and the result of the intersection based on the toolselected. For example, if the onscreen tool is a drill, the softwarewill determine the size, location, angle and depth of the hole based onthe diameter of the drill selected by the surgeon and the position ofthe drill relative to the patient model. The result of the intersectionbetween the onscreen tool and the patient model is illustrated in realtime (step 470) so that the surgeon can see the result of the virtualprocedure as it is performed.

In this way, the surgeon can use a virtual surgical tool to perform avirtual procedure and the virtual surgery computer will display theprogress of the procedure in real time. Further, if the tissue to beresected is identified on the model, as described above, the computershows the removal of such tissue as it is virtually resected. Forinstance, in the example in which the bone to be resected is displayedin red, the computer will show the removal of the red portion of thebone, as the surgeon virtually operates on the bone.

The surgeon can reset the patient model to restart the virtual procedureso that the surgeon can see the result of using different paths (step475). The surgeon can either re-set the entire procedure or just one ormore of the steps taken during the virtual procedure. For instance, thesurgeon can perform the surgical procedure along a first path or seriesof paths, and then perform the virtual surgery along a different path orseries of paths to determine which path is the optimum path to use forthe actual surgery. Additionally, since the surgical procedure willlikely include a plurality of paths (i.e. more than a single cut), thesurgeon can re-set a particular step rather than all of the steps in avirtual procedure. Specifically, if the surgeon performs a number ofsteps in a virtual procedure, the surgeon can re-set each step in seriesto step back through the procedure to alter one or more of the steps.For instance, after the seventh step the surgeon may be unhappy with theresult, so the surgeon may undo the previous two steps. The softwarethen resets the model so that it displays the result of the patient'smodel after the first five steps in the virtual procedure.

As described above, the surgeon performs a virtual procedure of one ormore steps by manipulating an input device to control the path of one ormore onscreen tool(s). After the surgeon is satisfied with the result ofthe virtual procedure, the surgeon verifies the virtual procedure toconfirm that the virtual procedure is to be used to create theinstructions for the surgical robot 200. The verification can be assimple as providing an input indicating that the virtual procedureperformed is to be used to create the instructions for the surgicalrobot.

As described above, the virtual surgery computer monitors the input ofthe input device during the virtual procedure. At the same time, thecomputer records various information for each step of the virtualprocedure. Specifically, for each step, the computer records the toolused, the path that the tool was displaced relative to the patientmodel, and the orientation of the tool relative to the patient model.

The path and orientation of the onscreen tool are determined relative toa reference point on the patient model. The reference point is used tocorrelate the patient model and the patient during the surgicalprocedure. In other words, the path and orientation of the onscreen toolfor each step of a procedure is determined relative to the referencepoint, and then the path and orientation of the surgical robot arecalculated to orient and displace the surgical robot relative to thereference point.

Based on the data recorded for each step of the virtual procedure, thecomputer calculates a series of instructions for the surgical robot. Theinstructions are exported to a server that is in communication with thecontrol computer. The instruction set is then uploaded to the controlcomputer to be used to control the surgical robot during a procedure.

To commence the actual surgical procedure, the position of the surgicalrobot is correlated with the reference point on the patient. After theposition of the robot is correlated with the reference point on thepatient, the surgeon commences operation of the surgical robot. Thecontrol computer controls the position and orientation of the surgicalrobot in response to the instruction set determined in step 485. In thisway the movement of the tool on the surgical robot parallels themovement of the onscreen tool as manipulated by the surgeon during thevirtual surgery. Specifically, based on the instructions set, thecontrol computer controls the movement of the surgical robot tool, sothat the displacement path and orientation of the surgical robot toolrelative to the reference point is substantially similar to thedisplacement path and orientation of the onscreen tool relative to thereference point on the patient model. Further, the control computercontrols the surgical robot so that the surgical robot follows theidentical or substantially the same sequence of steps that the surgeontook during the virtual surgery. Specifically, the control computercontrols the surgical robot so that the first step taken by the surgeonis the first step taken by the surgical robot; the second step taken bythe surgeon during the virtual surgery is the second step taken by thesurgical robot, and so on. In this way, the sequence of steps, alongwith the movement and orientation of the surgical robot tool is the sameas or substantially similar to the sequence of steps, and the movementand orientation of the onscreen tool used by the surgeon during thevirtual procedure.

In the foregoing description, the system has been described as includingtwo separate computers connected with a server. The advantage of such aconfiguration is that the virtual surgery performed to program thesurgical robot can be performed remotely from the operating area.However, the actual configuration of the system can vary. For instance,the virtual surgery computer can be directly linked to the controlcomputer, eliminating the need for a server. Alternatively, rather thanlinking the two computers, data from the virtual surgery computer can beexported to a storage medium and then uploaded to the control computer.For instance, the data, such as the instructions set can be exported toa optical disk, such as a CD or other memory device, and the controlcomputer may include a device for reading the data from the storagemedium. Further still, it may be desirable to use a single computer forboth the virtual surgery and to control the surgical robot, thuseliminating the need for two separate computers and a server. Inaddition, although the surgical robot has been described as beingcontrolled by a separate computer, the robot may be controlled by anintegrated microprocessor that receives the operating instructions andcontrols the robot, rather than a separate computer such as a personalcomputer.

Detecting Tool Deflection

As described above, the position detection device 120 can be used todetect and monitor the position of either a surgical tool 100 or asurgical robot 200. One issue in correctly navigating the surgical toolor the robot is the need for an accurate assessment of the position andorientation of the surgical tool or robot. Specifically, although anumber of markers 105 may be used to identify the position of a tool,markers are typically not applied to the tip of a tool, particularly ifthe tool is a cutting tool. Instead, the position of the tool isdetermined and the position of the cutting tip is calculated based onthe known geometry of the tool, and the presumption that the tool is arigid element. However, during use, the tool may deflect or deform sothat the actual position of the cutting tip may not correspond to thepresumed position of the cutting tip. Therefore, the correlation betweenthe actual tissue being cut and the virtual model do not match. In otherwords, based on the data received from the position detection device theOR computer 80 determines that a certain portion of tissue is resected,however, due to tool deflection the actual tissue resected may bedifferent.

To accurately identify the position of a tool during a procedure, thetool may include a sensor for detecting deflection or deformation of thetool. For instance, referring to FIG. 2, a surgical tool 100 isillustrated, having a cutting blade 102. The surgical tool 100reciprocates the cutting blade during operation. A sensor in the form ofa load-cell 104 included in the saw detects the force and/or torqueapplied to the blade. Alternatively, a piezoelectric sensor may beconnected directly to the blade to detect the force and/or torqueapplied to the blade. The measured force or torque is used to predictthe distance “d” that the blade bends. Specifically, properties of thecutting blade 102 are stored. Based on the predefined cutting toolproperties and the measured force or torque, the amount of bending iscalculated. The calculated amount of bending approximates the distance“d” and is used as a compensation factor to adjust the position of thecutting tool detected by the position detection device 120.

In the embodiment discussed above, the position of the cutting tool isconstantly calculated based on the measured position of the cutting tooland the measured amount of force or torque applied to the cutting tool.An alternative utilizes an onboard processor to calculate the tooldeflection and manipulate the position detection element(s) on thecutting tool. In this way, the position detection device 120 will detectthe compensated position of the cutting tool, which will reflect theactual position and orientation of the deflected cutting tool.

Referring again to FIG. 2, the surgical tool 100 may include a processor106 operable to receive signals from the load cell 104 indicative of theforce applied to the cutting blade. Based on the data received from theload cell, the processor 106 calculates the deflection “d” of the tip ofthe cutting tool 102.

As shown in FIG. 2, the surgical tool 100 includes an element fordetecting the position of the surgical tool. For instance, in thepresent instance, the surgical tool includes a reference frame ontowhich a plurality of markers 105 are mounted. As described previously,the position detection device 120 detects the position of the markers todetermine the location and orientation of the surgical tool.

In a system in which the deflection compensation is performed by eitherthe position detection device or the OR computer, the frame is typicallyrigidly mounted to the surgical tool so that the position of the markersrelative to the rest of the tool is fixed. However, as shown in FIG. 2,the frame 107 may be movably connected to the surgical tool 100.Although the freedom of movement of the frame may be limited, preferablythe frame is connected to the surgical frame by a connection thatprovides at least two degrees of freedom, such as a universal joint.

Connected to the frame 107 are a plurality of actuators or deflectors108 that control the position of the frame. The actuators 108 are inelectrical communication with the processor 106, and preferably theprocessor 106 independently controls the operation of each actuator.

The processor 106 controls the operation of the various deflectors 108based on the signals received from the sensor 104. Specifically, asdescribed above, the processor 106 calculates the deflection “d” of thetip of the cutting tool based on the signal received from the sensor104. Based on the calculated deflection, the processor determines theappropriate compensation to the position of the frame to compensate forthe deflection of the cutting tool 102. The processor then controls theoperation of the actuators 108 to re-position the frame. For instance,in the example illustrated in FIG. 2, the cutting tool is deflected anamount “d” in a clockwise direction. Accordingly, the actuators 108reposition the frame 107 to displace the markers 105 an amount “d” in aclockwise direction. The position detection device 120 then detects theposition of the surgical tool at the compensated position so that nofurther calculations are necessary to monitor the position of thedeflected cutting tool.

By utilizing an on board deflection compensation, the system canincorporate deflection compensation, while still allowing the surgicaltool to be used with a variety of commercially available positiondetection devices without the need to modify the software used by suchdevices.

Although the foregoing example describes the onboard compensationfeature as utilizing a plurality of actuators to reposition a referenceframe, the configuration of the compensation elements may vary dependingon the configuration of the position detection elements used.

For instance, other position detection devices may be used in thesystem, such as systems that include electromagnetic sensors, ultrasoundelements or accelerometers. When such elements are utilized, thecompensation features may either vary the position of the element or itmay vary the data provided by such elements in response to the datareceived regarding the load on the cutting tool.

Alignment Element for Surgical Tool

When performing a navigated freehand procedure as described above, oneof the issues is the time that a surgeon typically takes to align a cutbefore starting the cut. Frequently this alignment causes unnecessarydelay. To limit the delay caused during the alignment process, thesurgical tool may includes an alignment guide mounted on the surgicaltool. The position of the alignment guide 115 is known relative to thesurgical tool, so that the position detection device 120 can determinethe position of the alignment guide. Accordingly, using the virtualnavigation, the surgeon can watch the monitor 85 (or a screen mounted onthe instrument) to see the position of the blade relative to the targetpoint for the cut identified on the virtual model. When the tool isproperly aligned on screen, the tool is properly aligned on the patient.The guide is the anchored to the patient to align the tool for the cut.

Referring to FIG. 4, the alignment guide 115 is an elongated elementpositioned adjacent the cutting tool 102. The forward end of thealignment guide 115 is positioned so that the tip of the alignment guideprotrudes beyond the tip of the cutting tool. In the present instance,the alignment guide 115 includes a plurality of retractable pins orspikes 116 positioned at the end of the guide. The pins 116 areconfigured to anchor the guide 115 into bone. The alignment guide 115further includes a recess for receiving the pins 116 when the pinsretract so that the pins do not interfere with the cutting operation ofthe tool.

Although the alignment guide 115 can be configured in a variety ofshapes, in the present instance, the alignment guide is an elongatedflat bar positioned parallel to the cutting blade 102 and in closeproximity to the cutting blade. The guide 115 preferably is more rigidthan the cutting blade, and preferably is substantially rigid relativeto the cutting blade. In this way, the alignment guide supports thecutting tool limiting the deflection of the cutting blade toward theguide.

During a procedure, the alignment guide operates as follows. Asdescribed above, the surgeon views the monitor to properly align thesurgical tool to perform the cut. After the surgical tool is aligned,the surgical tool is anchored to the bone by driving the tool toward thepatient bone to anchor the pins 116 in the bone. The surgical tool mayinclude an internal hammering device to lock the anchoring pins 116 tothe bone when the alignment is correct, or the surgical tool can simplyinclude a contact portion, such as an anvil 118 that can be hammered todrive the pins 116 into the bone. As described below, during a cut, theguide 115 collapses. Accordingly, to anchor the pins into the bone, theguide 115 includes a brake or a lock to lock the guide in an extendedposition while the pins are anchored into the bone.

Once the guide 115 is anchored to the bone, the surgeon starts the tooland the cutting blade 102 is driven into the bone. The lock or brake onthe guide is released to allow the guide to collapse during a cut.Specifically, the guide 115 is configured so that it can collapse ortelescope as the saw is moved forward during the procedure. In otherwords, the pins 116 remain in engagement with the tissue (e.g. bone) andthe guide 115 collapses as the saw move forward relative to the pins. Inthis way, the pins 116 anchor the cutting blade 102 as the cutting bladeprogresses through a cut.

As described above, the alignment guide includes a flat bar andretractable pins. However, the configuration of the guide can vary basedon a number of criteria, including, but not limited to design, frictionand heat requirements, sterilization needs etc. For instance, ratherthan being an elongated flat bar, the guide may comprise a pair ofelongated cylindrical rods spaced apart from one another. The ends ofthe rods may be pointed to facilitate anchoring the guide into the bone,as shown in FIG. 5.

Navigable Marker

As described previously, the OR computer 80 may display a virtual modelof the portion of the patient on which the procedure is to be performed.Further still, the location of the patient may be registered tocorrelate the position of the patient with the virtual model. Inprevious descriptions, the virtual model of the patient was utilized toguide the surgeon in manipulating the surgical tool to perform thesurgery. Alternatively, the virtual model of the patient may be used toguide the surgeon in marking the operation site. The marking can then beused alone or in combination with the guided freehand system describedabove.

Referring to FIG. 13, a navigable marking pen 250 is illustrated. Thenavigable marking pen 250 includes one or more elements for detectingthe position and orientation of the marker. For instance, the markingpen may include a reference frame 257 and a plurality of positionmarkers 255 similar to the frame 107 and position markers 105 describedabove in connection with the surgical tool. The marking pen 250 can beguided by viewing the display of the OR computer 80 as described abovein connection with operation of the surgical tool 100. The marking pen250 is guided to draw lines on the bone at the appropriate locations asidentified on the virtual model.

The method for using the navigable marking pen 250 operates as follows.Prior to the procedure, a virtual model of the relevant portion of thepatient is created as discussed above. The surgeon analyzes the virtualmodel to determine the procedure to be performed and identifies theportion of the patient to be resected or otherwise operated upon duringthe procedure. For instance, in the instance of implanting a prostheticdevice, a femoral prosthetic may be implanted as previously described.The surgeon selects the appropriate prosthetic and aligns a model of theprosthetic over the operation site. Based on the model of the prostheticand the alignment, the Pre-op computer 70 may identify the tissue to beresected during the procedure. Prior to the procedure, the patient isregistered as described previously, so that the patient positioncorresponds to the virtual model. The OR computer 80 displays thevirtual model along with a model of the navigable marking pen and anindication of the tissue to be resected. As the surgeon manipulates themarking pen 250, the position detection device 120 detects the movementof the marking pen and provides data to the OR computer so that themodel of the marking pen moves on the screen relative to the patientmodel in real time. Accordingly, the surgeon manipulates the marking penso that the model of the marking pen aligns with the portion of thevirtual model indicated for resection. The surgeon manipulates themarking pen 250 so that the model of the marking pen traces the area ofthe virtual model identified for resection or other procedure (such asdrilling). In this way, the virtual model provides a guide for guidingthe surgeon to mark the appropriate areas on the patient on which theprocedure is to be performed. The surgeon may then simply perform theprocedure freehand using the markings on the patient as a guide or thesurgeon may perform the procedure using the markings and also usingfreehand navigation assistance as described above.

FIG. 13 also illustrates another potential improvement, in that themarking pen 250 may include a retractable pen that retracts when themarking pen is not aligned with the proper area on the patient. Byretracting, it is much less likely that the surgeon may erroneously markan incorrect area.

As shown in FIG. 13, the marking pen 250 includes a hollow housing 260having a generally open forward end. A displaceable pen 275 is disposedwithin the hollow housing 260. The pen is displaceable between anextended position and a retracted position. In the extended position thetip of the pen extends from the housing so that the tip of the pen canbe used to mark a surface. In the retracted position the pen isretracted into the housing so that the forward tip of the pen is withinthe housing so that the pen can not be used to mark a surface.

A spring 285 connected to the pen 275 biases the pen toward theretracted position. An actuator 280, such as a solenoid is operable toextend the pen forwardly against the bias of the spring. Specifically,when the solenoid is energized, the solenoid drives the pen to theextended position. When the solenoid is de-energized, the spring 285retracts the pen into the housing. Alternatively, the solenoid can beconfigured to drive the pen in both directions, i.e. the solenoid candrive the pen forwardly and rearwardly as desired.

The marking pen 250 is in communication with the OR computer 80 toreceive signals indicating whether the pen 275 should be extended orretracted. The marking pen may include a wired connection to the ORcomputer, however, in the present instance, the OR computer 80 includesa transmitter, and the marking pen includes a wireless receiver forreceiving signals from the computer. The marking pen 250 includes aprocessor 270 for receiving the signals from the computer andcontrolling the extension and retraction of the pen 275 in response tothe signals. Specifically, the processor 270 controls the operation ofthe solenoid to selectively energize and de-energize the solenoid inresponse to signals received from the OR computer.

The operation of the retractable marking pen 250 is similar to theoperation described above. However, the OR computer correlates the datafrom the virtual model with the data regarding the position of themarking pen. If the OR computer determines that the marking pen ispositioned over a portion of the patient that should be marked, thecomputer transmits a signal to the marking pen 250 indicating that thepen should be extended. The marking pen receives the signal and theprocessor 270 controls the solenoid, thereby energizing the solenoid toextend the pen tip 275. If the OR computer determines that the markingpen is position over a portion of the patient that is not to be marked,the computer transmits a signal to the marking pen indicating that thepen should be retracted and the processor control the solenoid toretract the pen. Alternatively, the processor may be configured so thatthe solenoid is energized only as long as the controller receives asignal indicating that the pen should be extended. In this way, the ORcomputer sends a signal to the marking pen as long as the computerdetermines that the marking pen is over a portion to be marked. As soonas the computer determines that the marker is over an area that is notto be marked, the computer ceases sending a signal to the marking pen.The processor then de-energizes the solenoid to retract the pen inresponse to the lack of signal.

As can be seen from the foregoing, the marking pen 250 can provide anaccurate and efficient method for marking cut lines and other markinglines for performing a procedure. Prior to the procedure, the surgeonmay utilize the guidance system to manipulate the marking pen byaligning the model of the pen with the area of the virtual model to beoperated on. While the surgeon maintains alignment of the virtual penwith the portions of the model indicated as proper marking lines (suchas the outline of a prosthetic), the OR computer sends a signal to themarking pen indicating that the pen element 275 should be extended. Asthe surgeon maintains the virtual pen aligned on proper parts of thevirtual model, the marking pen 250 marks the patient. If the surgeonmanipulates the pen so that the virtual pen moves out of alignment withthe proper parts of the virtual model, the OR computer sends a signal tothe marking pen (or ceases sending a signal to the pen as describedabove) and the pen tip 275 retracts into the housing so that the penstop marking the patient. In this way, the surgeon controls theretraction of the pen by maintaining alignment of the virtual pen withthe portion or portions of the model the were identified during thepre-operative analysis as portions to be marked.

Tool Registration Head

An important step during navigated surgery is the accurate registrationof the surgical tools. If a tool is not properly registered thenavigation of the tool will be flawed leading to errors during theprocedure.

Referring to FIG. 14 a tool registration head 300 is illustrated. Theregistration head 300 is configured to cooperate with a plurality oftools 320 that are configured to be mounted in a plurality of sockets inthe head. The sockets are configured so that each socket cooperates witha particular tool. In this way, the system identifies the tool type inresponse to a determination of the socket into which the tool ismounted. For instance, the registration head 300 may include first 312,second 314 and third sockets 316, each having a different configuration.A first tool is configured to mate with the configuration of the firstsocket, a second tool is configured to mate with the configuration ofthe second socket and a third tool is configured to mate with theconfiguration of the third socket. Each socket further includes a sensorindicating whether a tool is registered in it or not. If the sensor inthe first socket indicates the presence of a tool, the system determinesthat the first type of tool is mounted in the registration head.Similarly, if the sensor in the second or third socket detects thepresence of a tool, the system identifies the tool as being the secondor third type accordingly.

Alternatively, rather than including a sensor in each slot, theregistration block may include a plurality of detection element 310,such as reflective spheres, as shown in FIG. 14. The location of eachslot relative to the detection elements is known. Therefore, byinserting the surgical tool into the appropriate registration slot, theposition of the surgical tool relative to the registration block isknown. Based on this position data, the processor is able to determinewhich registration slot the surgical instruments was inserted into,thereby identifying the instrument.

Additionally, as described above, the various registration slots mayvary depending on the type of instrument used, as well as the size ofthe instrument. For instance, in FIG. 14, the registration block includeseveral holes of varying size 312 a,b,b. By inserting the instrumentinto hole 312 a, the system detects that the instrument is a pointer ordrill bit or a diameter corresponding to hole 312 a. Similarly, slots314 a,b,c are used to indicate that the instrument is a saw of aparticular thickness.

Further, the sockets 310 and the tools may also be configured so thateach tool will only mount in a particular orientation. In other words,each tool fits into a particular socket in a particular orientation. Inthis way, by simply identifying which socket a tool is mounted in, thesystem can determine the tool type and orientation.

The registration head is in communication with the OR computer 80 or theposition detection device 120 so that the registration head cancommunicate signals to the system indicative of the tool registered inthe head. The system may maintain a data file for each tool typeindicating the profile and operating parameters for each tool. In thisway, when the system identifies the tool registered in the head 300, thesystem has the relevant data regarding the size, configuration etc. ofthe tool so that the system can monitor the position of the toolaccordingly.

Identifying Regions of Waste Material

As described previously, the present system 50 could be utilized toperform guided freehand surgery in which a model of the patient isprovided, along with a model of the surgical tool and the models can beused to guide the surgeon during the actual procedure. For instance, thepatient model may include a portion identified as tissue to be resected.The system tracks the movement of the surgical tool 100, so that whenthe surgeon moves the tool, the system displays the movement of the toolin real time on the monitor. In this way, the surgeon can align the toolwith the patient by aligning the model of the tool with the portion ofthe patient model identified for resection. In this way, the surgeon canfollow the onscreen guidance to resect a portion of tissue.

When resecting a portion of a bone a surgeon may cut more rapidly andaggressively when the cutting tool is relatively far from the boundaryof the area to be resected. As the surgeon approaches the boundary ofthe resection area, the surgeon may slow the pace of cutting to ensurethat the resection remains within the desired boundaries. To help thesurgeon readily assess the proximity to the resection boundary, thesystem may provide indicators and warnings to the surgeon as the surgeonapproaches the boundary. Further still, the system may be configured tocontrol the operation of the surgical tool 100 in response to theproximity of the tool to the resection boundary.

As described above, the system provides for the pre-operative analysisof a patient model and the identification of the tissue to be resected.After the portion of the tissue to be resected is determined, the systemmay analyze the data for the model and identify the boundary for theresection. The tissue to be resected may then be identified with aplurality of colors based on the relation to the resection boundary.

For instance, the portion of the tissue that is not to be removed may beillustrated in red. A portion of the tissue that is to be resected thatis relatively close to the resection boundary may be illustrated inyellow. The remainder of the tissue to be resected may be illustrated ingreen. In this way, as the surgeon views the model during a procedurethe surgeon may cut rapidly and aggressively while the system indicatesthe tool is operating on tissue in the green zone. As the surgeonapproaches the resection boundary, the model illustrates the tool asoperating on tissue in the yellow zone. This serves as an indication tothe surgeon to proceed more slowly as the tool approaches the resectionboundary. In this way, the system provides a readily identifiablegraphical display that informs the surgeon of the proximity of thesurgical tool to a resection boundary. Similarly, the system can be usedto identify the proximity of the surgical tool to sensitive anatomicalstructures, such as nerves, vessels, ligaments etc. The anatomicalstructures can be illustrated in red and the tissue proximate thestructures can be identified in yellow as an indicator to the surgeonthat the cutting tool is getting close to the sensitive structure.

In addition to providing a graphical indication of the proximity to aresection boundary, the system may provide a graphical and/or audiblewarning to the surgeon. For instance, as the system detects the surgicaltool approaching the area proximate the resection boundary (i.e. theyellow zone), the system may display a graphical warning on the monitor85 in addition to illustrating the surgical tool in a yellow zone oftissue on the model. Alternatively or in addition to the graphicalwarning, the system may provide an audible warning indicating that thecutting tool is approaching the desired boundary. The system may provideyet another warning in the event the cutting tool is detected at orbeyond the desired boundary. In other words, if the surgical tool entersthe red zone the system may provide a further warning.

The system may also be configured to control the operation of thesurgical tool in response to a determination of the position of thesurgical tool relative to the desired boundary. Specifically, if thesystem determines that the tool is positioned within the tissue to beresected that is not proximate the boundary (i.e. in the green zone),the system may allow the surgical tool to controlled as desired by thesurgeon. If the system determines that the tool is positioned within thetissue to be resected that is proximate the boundary (i.e. the yellowzone), the system may reduce or attenuate the operation of the surgicaltool. For instance, if the tool is a saw, and it enters the yellow zone,the system may slow down the reciprocation or revolution of the saw asit moves proximate the resection boundary. Further still, if the systemdetects that the tool is positioned at the boundary or on tissue that isnot to be resected or operated on, the system may control the surgicaltool by completely stopping the tool. Although the system mayautomatically control the operation of the surgical tool, the systemincludes an override function that allows the surgeon to override thecontrol of the tool. In this way, if the surgeon determines that aportion of tissue should be resected that was not identified forresection during the pre-operative analysis, the surgeon can overridethe system and resect the tissue during the procedure.

Yet another feature provided by identifying operating parameters fordifferent areas of tissue is the ability to automatically vary the viewdisplayed on the monitor during a procedure. For instance, when thesystem detects the surgical tool in a first area of tissue, the monitormay display a first view, whereas, when the system detects the tool in asecond area of tissue, the monitor may display a second view.Specifically, if the system detects the surgical tool in the green zoneportion of tissue, the system may display a wide angle or low zoom viewso that the surgeon can view more of the area being operated on. As thetool enters the yellow zone, the system may change the view to a moremagnified view so that the surgeon can see the details of the cut moreclearly as the tool approaches the resection boundary. If the surgeonprefers different views than the ones automatically presented by thesystem, the surgeon can manually select a different view. Additionally,the system may query the surgeon as to whether the selected view shouldbe the default view for the particular zone of tissue. If the surgeonresponds in the affirmative, the system changes the default view for theparticular user, so that the new view is displayed for the user when thecutting tool enters the corresponding type of tissue. In this way, thesystem can automatically change the view based on detectedcharacteristics of a procedure and user preferences.

Another feature that may assist in guide the surgeon during a procedurerelates to the representation of the tool of the surgical instrument.For instance, in the situation of a cutting tool, such as a saw, thecutting tool is a generally flat rectangular element. If the plane of acut is illustrated by a line through a portion of tissue, it may bedifficult to assess the angle of the cutting blade to ensure that thecutting blade is aligned with the plane of the appropriate cut.Accordingly, the cutting blade may be illustrated as an oval on thedisplay. The shape of the cutting blade then depends on the angle of thecutting blade relative to the proper plane. If the cutting blade isaligned properly the cutting blade will look similar to a line. As thecutting blade is twisted relative to the proper cutting plane, thecutting blade appears more rounded and oval. In this way, the variationbetween the angle of the cutting blade and the angle of the propercutting plane is readily apparent based on the ovality of how thecutting tool appears on the display.

Registration Pointer with Surface Contact Detection

As previously described, when registering the position of the patientprior to a procedure, a portion of the patient is scanned to identifyone or more anatomical landmarks or features. Such features or landmarksare utilized to correlate the patient position with the virtual modelcreated for the patient. One method for acquiring the registration datautilizes a navigational pointer that the surgeon traces over portions ofthe patient. However, when the surgeon is tracing the surface, the tipof the pointer may come out of contact with the surface of the patient.This is particularly true when tracing over soft tissue or when tracingalong curved surfaces. If the pointer is not in contact with the surfaceof the relevant portion of the patient the resulting data points will beerroneous.

To improve the accuracy of the data collected during registration, thesystem may include a pointer that incorporates a surface contactdetection element. If the pointer is out of contact with the surface ofthe relevant portion of the patient, the points are ignored during theregistration analysis.

Referring to FIG. 15 an improved registration pointer is designated 350.The pointer is an elongated element having a tip configured to contactthe relevant portion of a patient. The pointer 350 is operatively linkedwith the position detection device 120. The operative link may be awireless connection in which the pointer includes a wirelesstransmitter. Alternatively, the pointer may be connected directly to thedetection device via a cable.

The pointer includes a sensor 360 for detecting whether the tip of thepointer is in engagement with the patient or whether the tip of thepointer is spaced apart from the patient. One possible sensor 360 is animpedance sensor. Alternatively, the sensor may be a simple forcetransducer. The pointer 350 includes a circuit 365 for analyzing thesignal from the sensor and determining whether the pointer is in contactwith the patient surface based on the signal from the sensor. The datafor the point or points in which the pointer was out of contact with thepatient surface are not utilized during the registration process.Specifically, the pointer circuit may identify valid and invalid data byvarious means, including a first method in which the pointercommunicates the relevant data to the position detection device 120 viaa wired or wireless connection. Alternatively, the pointer circuit maycontrol the position tracking elements so that the pointer is out ofview of the position detection device 120 when the pointer 350 is out ofcontact with the patient surface.

In the instance in which the pointer circuit communicates directly withthe position detection device, the pointer circuit evaluates whether thepointer is in contact with the patient based on the signal received fromthe sensor 360. If the circuit determines that the pointer is out ofcontact, the circuit communicates a signal to the position detectiondevice 120 indicating that the data points are invalid. In this way, aslong as the pointer remains out of contact with the patient surface, theposition detection device receives a signal from the pointer indicatingthat the points are invalid and should be ignored.

Alternatively, the pointer may control the position detection elementsto essentially make the pointer disappear from view of the positiondetection device 120 when the pointer is out of contact. Since thepointer is out of view when it is out of contact with the patient, nodata is collected while the pointer is out of contact. The steps forrendering the position detection elements out of view of the detectorvaries depend on the type of detection element. For instance, asdescribed previously, the position detection device may operate inconjunction with passive and active markers. An active marker is amarker that transmits an infrared signal to the detection device and theposition of the marker is identified by triangulating the receivedsignal. Accordingly, to control the active marker(s), the pointercircuit 365 controls the active markers by turning off the activemarkers so that they no longer emit an infrared signal when the pointeris out of contact with the relevant portion of the patient. While theemitter ceases emitting infrared light, the marker is hidden from theposition detection device 120 so that the registration points are notdetected.

If the markers on the pointer are passive elements, the markers aredetected by detecting the infrared light reflected back to the positiondetection device 120. In order to hide such passive markers the pointercircuit may be used to control one or more elements including adisplaceable opaque surface and an electronically/chromatically actuatedeffect to disable the infra-red reflectivity of the ball.

Automatic Selection of View

During a procedure, the surgeon is able to manipulate the view of thepatient model to view the model from any desired angle or magnification.Furthermore, the system may be configured to automatically select theappropriate view based on the status of the procedure and informationregarding the surgeon's preferences.

As described above, the system is operable to track the position of thesurgical instrument 100 and correlate the position of the tool relativeto a virtual model of the patient. Additionally, the virtual model mayindicate the portions of the patient that are to be operated on. Forinstance, the virtual model may identify the boundaries of the tissue tobe resected during a procedure. The tissue to be resected may include anumber of portions along a number of planes.

When resecting the various portions it may be desirable to modify theview of the virtual model displayed on the monitor. For instance, whencutting along a first plane it may be desirable to view the virtualmodel from a first perspective, and when cutting along a second plane itmay be desirable to view the virtual model from a second perspective.Accordingly, the system tracks various data regarding the status of aprocedure, including, but not limited to the following: the position ofthe surgical tool relative to the tissue to be resected and theorientation of the surgical tool relative to the tissue to be resected.Based on the position and orientation of both the tissue and thesurgical tool, the system calculates which surface is about to be cutduring the procedure.

The system is pre-programmed so that certain views are shown by defaultfor certain cuts. For instance, returning to the example of resecting afemur in preparation for a femoral prosthetic for a TKR procedure,several surfaces are to be cut, as shown in FIG. 10. Each surface may bebest viewed from a different perspective during the procedure. Whencutting the anterior surface of the medial condyle a first view may bedesirable, whereas when cutting the anterior surface of the lateralcondyle a second view may be desirable. Accordingly, the system sets apre-defined first view for viewing the virtual model when the anteriorsurface of a medial condyle is resected. Similarly, default views can bedefined for a number of common resection procedures. When the systemdetermines the cut to be performed, the system determines the best matchfor the cut and displays the default automatically without theintervention of the surgeon.

Further, the system can be configured to account for the preference ofeach user. Specifically, a surgeon may desire a different view than thedefault view for a particular resection step or cutting plane. Thesystem allows the surgeon to override the default selection and specifythe view for a particular cut. The system stores the informationregarding the desired view for the particular cut for the particularsurgeon and uses the view as the default view in the future when thesystem determines that a similar cut is to be made. The system tracksthe user preference based on the user logged into the machine.

In addition to automatically changing views based on certain pre-definedpresumptions, the system can be programmed to identify the particularviews to be displayed during a procedure. For instance, during thepre-op analysis of the patient's model, the surgeon may identify theview to be displayed for each portion of the procedure. For example,during the resection of the bone for a TKR, the surgeon may identify theview to be displayed for each of the different cuts to be made during aprocedure. These preferences can be saved to the profile for the userand used in other future procedures, or the information can simply beused for the particular procedure. As the procedure proceeds, the systemtracks the surgical tool, determines the surface that is going to be cutand displays the virtual model using the view chosen for the surfaceduring the pre-op procedure.

Referring now to FIG. 3 another embodiment of a computer aided systemwith a surgical instrument 500 is illustrated. The surgical instrument500 is operable to assist in automated surgery in a surgical suite asdiscussed above in connection with the surgical instrument 100 describedabove. For instance, as described above, the system may include positiondetection device 120 that operates to detect the position of thesurgical instrument 500 relative to the patient. In the presentinstance, the position detection device detects the position of one ormore markers 505 on the surgical instrument and one or more markersconnected to the patient. In addition to the aspects, the surgicalinstrument 500 incorporates a number of features on the instrumentitself so that the instrument can be used to perform a number offunctions. Additionally, the surgical instrument may incorporatewireless communication with the OR computer 80.

Referring to FIG. 3 the surgical instrument 500 includes a tool, such asa saw 510, a microcontroller 515 for monitoring and controllingoperation of the tool 510, and a wireless unit 520. The instrument 500also includes an antenna 525. The wireless unit 520 and antenna 525allow the instrument to send data to the OR computer 80 regardingmultiple status parameters, such as blade bending, saw speed and batterycharge. In addition, the OR computer 80 includes a wireless unit 86,such as a bluetooth wireless element, and an antenna 87. The wirelessunit 86 and antenna 87 allow the OR computer to send and receive datawirelessly to and from the surgical instrument 500.

As described previously, the OR computer may be used to guide thesurgeon's operation of the surgical tool during a procedure. Forinstance, the system may track the position of the surgical tool in realtime and turn on or off the surgical tool depending on whether the toolis in proper alignment. For instance, if the system detects that thesurgical tool is adjacent an area to be resected, the system may send asignal wirelessly to the tool. If the tool does not receive such asignal, the tool will not operate. Specifically, the surgical tool mayhave a manual switch that the surgeon can manually turn on to operatethe tool. However, the tool will only run if both the manual switch isswitched to the on position and if the tool also receives a signalindicating that the tool is properly positioned to perform a procedure.If either the surgeon switches the tool off or if the tool does notreceive a signal indicating that the tool is properly positioned, thetool will not turn on for cutting.

As described above, the tool 500 may receive signals wirelessly tocontrol operation of the tool. In addition to signals controlling theon/off function of the tool, signals may also be used to control otheroperation of the tool. For instance, the tool may receive signals thatoperate to control the speed of the tool. For example, as describedabove, the system may track the position of the tool, so that the systemcan track whether the tool is adjacent a cutting boundary for a desiredprocedure. As the tool approaches the boundary, the system may send asignal to the tool indicating that the tool should be attenuated toreduce the speed of the tool. The circuitry in the tool 500 thenattenuates the operation of the tool in response to the wireless signal.

As described above, the surgical tool 500 may be controlled in responseto wireless signals from the OR computer 80. In addition, operation ofthe system may be controlled by signals from the surgical tool, which inthis instance are wireless signals. For instance, the surgical tool mayinclude various actuators, such as buttons, a joystick or a mouse ball.The operation of such actuators may be used as input signals to controloperation of the OR computer. For example, operation of a joystick onthe surgical tool 500 may send signals to the OR computer 80, causingthe graphics displayed on the display 85 to scroll in a particulardirection. Similarly, one or more buttons can be programmed to sendwireless signals to change the perspective or magnification of thegraphic being displayed.

In addition to including actuators, the surgical tool 500 may include adisplay 530 or view screen as shown in FIG. 16. Specifically, asdescribed above, the tool may include a wireless connection forreceiving data from the OR computer 80. The OR computer may transmitgraphics data to the tool so that the display 530 may display the samegraphics as are displayed on the main OR computer 80 display 85.Alternatively, the display 530 may display an alternate view to thegraphic being displayed on the OR computer display 85. In this way, thedisplay screen 530 may be used to guide the surgeon during a procedurein the same way that the OR computer display 85 may be used to guide thesurgeon.

As previously discussed, preferably a pointer is provided foridentifying reference points on the patient. Although the pointer hasbeen described as a separate element, the pointer may be integrated intothe surgical tool. For instance, since the configuration of the sawblade is known, the tip of the saw blade can operate as a pointer.Alternatively, a dedicated pointer may be incorporated onto the surgicaltool. It may be desirable to configure the pointer so that it can beextended and retracted as necessary so that the pointer can be readilyused, while not interfering with the operation of the cutting toolduring a procedure.

The operation of the pointer element may operate in conjunction with anactuator on the surgical tool. For instance, the tool may include abutton for indicating that the pointer is positioned at a referencepoint. When the surgeon positions the pointing element at a point to beregistered, the surgeon simultaneously presses the button, sending asignal to the OR computer indicating that the point is to be registeredas a reference point. The OR computer detects the position of thesurgical tool as determined by the position detection device, and storesthe data regarding the location of the reference point. In this way, theOR computer stores information regarding the position of the surgicaltool in response to actuation of the button on the surgical tool.

Cutting/Filing Blade

Referring to FIGS. 18-19 an alternate cutting blade 102′ is illustrated.The cutting blade 102′ has alternate surfaces on the body of the blade.The first side A is smooth as with a conventional blade; the oppositeside B of the blade is formed with a plurality of cutting surfaces toform a filing surface. The smooth side is used against the useful(remaining) bone when pure edge cutting is required. The blade isflipped (e.g. by turning the oscillatory saw head 180 degrees) whencutting and filing (or filing only) is required against the usefulremaining bone. The bide then acts as a navigated file but with acutting edge as well. The cutting edge/tip and filing surface featurescombine to make the navigated saw more effective for advanced navigatedfreehand bone cutting. The filing surface can act as a navigated testingplane to measure alignment accuracy of the surface and refine it byfiling.

It will be recognized by those skilled in the art that changes ormodifications may be made to the above-described embodiments withoutdeparting from the broad inventive concepts of the invention. It shouldtherefore be understood that this invention is not limited to theparticular embodiments described herein, but is intended to include allchanges and modifications that are within the scope and spirit of theinvention as set forth in the claims.

What is claimed is:
 1. A hand held surgical tool comprising: a housinghaving a distal end and a proximal end; a shaft having a distal endadapted to engage tissue at a pre-determined surgical site, the shaftdisposed within and moveable relative to an interior portion of thehousing; an actuator coupled to the shaft and configured to providecontrollable movement of the shaft relative to the distal end of thehousing; one or more elements coupled to an exterior portion of thehousing for use in detecting a position and orientation of the surgicaltool; and a processor attached to or coupled to the housing, theprocessor in communication with the actuator and having instructions tocontrol the operation of the actuator for controllable movement of theshaft in response to a signal received from a surgical computer.
 2. Thetool of claim 1, wherein the signals received by the processor tooperate the actuator are based on a surgical plan for a patient anatomywithin the pre-determined surgical site and a position and orientationof the surgical tool relative to the patient anatomy within thepre-determined surgical site, the position and orientation obtainedusing the one or more elements.
 3. The tool of claim 2, wherein thesurgical computer is configured to correlate the position andorientation of the surgical tool to the surgical plan for the patientanatomy within the pre-determined surgical site.
 4. The tool of claim 2,wherein when the distal end of the shaft is engaged with tissue aportion of the patient anatomy in the pre-selected surgical site ismarked.
 5. The tool of claim 4, wherein the patient anatomy is a bone.6. The tool of claim 5, wherein the mark comprises a visible mark. 7.The tool of claim 1, wherein the one or more elements for detecting theposition and orientation of the surgical tool are part of a referenceframe.
 8. The tool of claim 1, wherein the one or more elements fordetecting the position and orientation of the surgical tool include aplurality of position markers.
 9. A surgical system comprising the toolof claim 1, further comprising an optical tracking system configured tooptically track the one or more elements to detect the position andorientation of the surgical tool.
 10. The surgical system of claim 9,wherein the optical tracking system is configured to communicate theposition and orientation of the surgical tool to the surgical computer.11. A surgical system comprising the tool of claim 2, further comprisinga monitor configured to display the movement of the hand held surgicaltool in real time.
 12. The surgical system of claim 11, wherein themonitor is further configured to display a portion of the surgical planfor the patient anatomy within the pre-determined surgical site.
 13. Thesurgical system of claim 12, wherein the patient anatomy is a portion ofa femur or a tibia or a knee.
 14. The tool of claim 1, wherein theprocessor communicates with the surgical computer through a wiredconnection.
 15. The tool of claim 1, wherein the processor communicateswith the surgical computer through a wireless connection.
 16. The toolof claim 1, wherein the actuator is an electromechanical actuator. 17.The tool of claim 1, wherein the range of the actuator movement isconfigured to extend the distal end of the shaft past the distal end ofthe housing.
 18. The tool of claim 2, wherein the surgical plan includesa plan for a total knee replacement surgery.
 19. The surgical tool ofclaim 1, wherein the hand held surgical tool includes a surface formanually grasping the device.
 20. A surgical system comprising: asurgical computer; a hand held surgical tool comprising: a housinghaving a distal end and a proximal end; a shaft having a distal endadapted to engage tissue at a pre-determined surgical site, the shaftdisposed within and moveable relative to an interior portion of thehousing; an actuator coupled to the shaft and configured to providecontrollable movement of the shaft relative to the distal end of thehousing; one or more elements coupled to an exterior portion of thehousing for use in detecting a position and orientation of the surgicaltool; and a processor attached to or coupled to the housing, theprocessor in communication with the actuator and having instructions tocontrol the operation of the actuator for controllable movement of theshaft in response to a signal received from a surgical computer; and amonitor for displaying the position of the hand held surgical tool. 21.The surgical system of claim 20, further comprising an optical trackingsystem configured to optically track the one or more elements fordetecting the position and orientation of the surgical tool.
 22. Amethod for marking a patient, the method comprising: creating a threedimensional representation of a portion of the patient to which a boneor tissue cutting procedure is to be performed; identifying an area ofthe three dimensional representation corresponding to a portion of boneor tissue for which the procedure is to be performed; tracking a guidedsurgical tool to determine a position and orientation of the toolrelative to the portion of bone or tissue; marking a portion of the boneor tissue with a tissue engaging portion at a distal most end of a shaftextending from the guided surgical tool; and operating an actuatorcoupled to a housing of the guided surgical tool in response to anindication that the tissue engaging portion of the distal most end ofthe shaft is in an undesired position, the operating step providingrelative movement between the shaft and the housing to preventengagement of the distal most end of the shaft with the bone or tissue.23. The method of claim 22, wherein the surgical tool is a freehandsurgical tool.
 24. The method of claim 22, wherein marking includesmodifying a surface of the portion of the bone or tissue.
 25. The methodof claim 22, further comprising comparing the three dimensionalrepresentation of the portion of the patient to the position andorientation of the tool using a surgical computer.
 26. The method ofclaim 22, wherein tracking the surgical tool includes using an opticaltracking system to track a reference frame on the surgical tool.
 27. Themethod of claim 22, further comprising guiding the surgical tool to markthe portion of bone or tissue with an outline corresponding to a shapeof a preselected prosthesis.
 28. The method of claim 27, wherein theprosthesis is a femoral implant.
 29. The method of claim 21, furthercomprising guiding the surgical tool to mark the portion of bone ortissue with lines corresponding to cut planes for a total kneereplacement procedure.
 30. The method of claim 29, further comprisingpreselecting the lines corresponding to cut planes based on the threedimensional representation of the portion of the patient and aconfiguration of a preselected prosthesis.